Recently I was struggling to resolve ORA-12514 error, after I solved that there is a another error "TNS-12535: TNS: operation timed out". For your information in my machine I have disabled firewall & also added SQLNET.EXPIRE_TIME = 10. But the problem is still persists. Again all your help is needed. It is realted to Linux & Oracle 9.2.0.
have you configured your tnsnames.ora file?
He already worked on that. This is a network error.
try setting the connect_timeout_listener_name parameter in listener.ora to 0.
Are you absolutely sure the port numbers match (like 1521 everywhere)?